The present invention relates generally to stacked film components, devices that employ the components, methods of manufacturing the devices and/or the components, and, in particular embodiments, methods of recording and/or reading holograms on a device that incorporates aspects of the present invention.
Micro-holographic data storage enables large numbers of data layers in a single disc to achieve high data capacity. In each of the data layers, digital data “0” or “1” is represented by a presence or absence of a micro-hologram. The micro-hologram functions as a local reflector upon readout beam illumination. Presence or absence of a micro-hologram provides a “high” or “low” reflected signal that provides stored information.
Optical recording of a micro-hologram requires two counter-propagating focused coherent laser beams from both sides of the disc with overlapping focal regions. Interference of the two beams at the focal region induces local changes of the material that results in a refractive index modulation pattern, which is the micro-hologram. Good alignment of these two beams typically requires a five-axis servo system during dynamic recording. In addition, recording at all the layers through the depth of the disc requires a well aberration compensated optical system, which is very challenging at high numerical aperture. Therefore, both the optics and servo system are much more complicated and expensive than what are required in conventional optical drive systems where only a single focused beams is used for recording and/or readout.
The concept of “pre-format” was proposed to overcome this issue. (See e.g., U.S. Pat. No. 7,388,695). In this scheme, blank discs are “pre-formatted” with the micro-hologram layers before being used in an optical drive. This “pre-format” step is one of the steps in disc manufacturing. The preformatted discs are then used in an optical drive for recording and readout. The recording is done through erasure or modification of the micro-holograms using a single focused laser beam. The system for “pre-formatting” is a high quality expensive dual-side micro-hologram recording system.
Accordingly, there is an ongoing opportunity for improving upon existing optical data storage structures, methods of manufacture, methods of recording, and/or methods for reading.